There is evidence to suggest that the genesis of atherosclerosis is in childhood; thus, it is important to identify risk factors in early life so that preventive measures can be established. It has been hypothesized that the high cholesterol content of breast milk sets up homeostatic mechanisms that allow for effective cholesterol metabolism in adult life. Commercial formula (low in cholesterol) is currently the predominate infant milk feeding mode in the U.S. Few studies have examined the relationship between infant milk feeding and serum cholesterol levels beyond infancy. This epidemiologic study is designed to examine the relationship between type of infant milk feeding (human milk, cow's milk, or commercial formula) and serum cholesterol levels of U.S. children aged 4-11. The data source is the National Center for Health Statistics' first National Health and Nutrition Examination survey 1971-1974 (NHANES I). These data (N=3249) contain the only currently available information on both type of infant feeding and serum cholesterol levels for a representative sample of U.S. children. Multivariate techniques will be used to examine the effects of current age, sex, race, parental income, parental education, current weight status, current diet, and age of introduction of solid foods on the relationship between type and duration of infant milk feeding and childhood serum cholesterol levels. This study offers a number of advantages over previous studies of early infant milk feeding and serum cholesterol levels in childhood: a large heterogenous sample, inclusion of important confounding factors such as current diet and weight, a broad childhood age span, and generalizability of results to the U.S. population. Findings from this study will be important for identifying early dietary determinants of childhood serum cholesterol levels.